PH-5110-5KN 설치형 pH측정기 Double Junction Glass pH 전극 PH-5110-5KN 설치형 pH측정기 Double Junction Glass pH 전극 PH-5110-5KN 설치형 pH측정기 Double Junction Glass pH 전극 PH-5110-5KN 설치형 pH측정기 Double Junction Glass pH 전극 PH-5110-5KN 설치형 pH측정기 Double Junction Glass pH 전극